Dynamically sized redundant write buffer with sector-based tracking

ABSTRACT

Exemplary methods, apparatuses, and systems include detecting an operation to write dirty data to a cache. The cache is divided into a plurality of channels. In response to the operation, the dirty data is written to a first cache line in the cache, the first cache line being accessed via a first channel. Additionally, a redundant copy of the dirty data is written to a second cache line in the cache. The second cache line serves as a redundant write buffer and is accessed via a second channel, the first and second channels differing from one another. A metadata entry for the second cache line is updated to reference a location of the dirty data in the first cache line.

TECHNICAL FIELD

The present disclosure generally relates to maintaining and trackingdata and redundant copies of data within a cache, and more specifically,relates to a dynamically sized redundant write buffer within a cachewith sector-based tracking.

BACKGROUND ART

A memory subsystem can include one or more memory devices that storedata. The memory devices can be, for example, non-volatile memorydevices and volatile memory devices. In general, a host system canutilize a memory subsystem to store data at the memory devices and toretrieve data from the memory devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousembodiments of the disclosure. The drawings, however, should not betaken to limit the disclosure to the specific embodiments, but are forexplanation and understanding only.

FIG. 1 illustrates an example computing environment that includes amemory subsystem in accordance with some embodiments of the presentdisclosure.

FIG. 2 illustrates an example of redundant write buffers within a cache.

FIG. 3 illustrates an example organization of metadata for a redundantwrite buffer.

FIG. 4 illustrates an example of metadata for a redundant write bufferas shown in FIG. 2 .

FIG. 5 illustrates another example organization of metadata for aredundant write buffer.

FIG. 6 illustrates yet another example organization of metadata for aredundant write buffer.

FIG. 7 is a flow diagram of an example method to write redundant dirtydata to a cache in accordance with some embodiments of the presentdisclosure.

FIG. 8 is a flow diagram of an example method to recover data using aredundant write buffer in accordance with some embodiments of thepresent disclosure.

FIG. 9 is a flow diagram of an example method to track the migration ofdirty data between caches using a redundant write buffer in accordancewith some embodiments of the present disclosure.

FIG. 10 is a flow diagram of an example method to copy dirty data tonon-volatile media using a redundant write buffer in accordance withsome embodiments of the present disclosure.

FIG. 11 is a block diagram of an example computer system in whichembodiments of the present disclosure may operate.

DETAILED DESCRIPTION

Aspects of the present disclosure are directed to a memory subsystemmaintaining and tracking data and redundant copies of data within acache. In particular, embodiments implement a dynamically sizedredundant write buffer within a cache with sector-based tracking. Amemory subsystem can be a storage device, a memory module, or a hybridof a storage device and memory module. Examples of storage devices andmemory modules are described below in conjunction with FIG. 1 . Ingeneral, a host system can utilize a memory subsystem that includes oneor more components, such as memory devices that store data. The memorydevices can include, for example, non-volatile memory devices (e.g.,NAND). Other types of memory devices, including volatile memory devices,are described in greater detail below in conjunction with FIG. 1 . Thehost system can provide data to be stored at the memory subsystem andcan request data to be retrieved from the memory subsystem.

A cache is a volatile memory component that can fulfill read requestsfaster than a non-volatile memory component. For efficiencies in costand speed, the size of a cache is small relative to the underlyingnon-volatile memory. In some caches, memory subsystems write new andupdated data values to the cache first, mark the data as dirty, andlater write the data to non-volatile memory in accordance with acleaning, eviction, or another policy. Should an uncorrectable error orother failure occur resulting in an inability to read the data while itis still dirty, the data is lost. Some systems require high reliabilitybut are limited in the level of error checking and correction that canbe used to recover data.

Aspects of the present disclosure address the above and other issues byefficiently maintaining and tracking redundant copies of dirty datawithin the cache. For example, embodiments write an original copy ofdirty data to a first cache line and a redundant copy of dirty data to asecond cache line. The second cache line serves as a redundant writebuffer and is accessed via a separate channel than the first cache linefor increased reliability. The first and second cache lines can share acommon or otherwise use a consistently predictable addressable unit tosimplify the tracking of redundant copies. For example, if the first andsecond cache lines have common set values, embodiments can limittracking redundant copies to referencing a way value and sector value. Ametadata entry associated with the second cache line references thelocation of the dirty data in the first cache line using this simplifiedapproach. As a result, memory subsystems can provide high reliability indirty data.

Some memory subsystems utilize multiple layers of caches, e.g., asector-based cache layer and a page cache layer. A sector-based cachedivides the cache into addressable units, including channels, sets,ways, and sectors. In contrast, a page cache divides the cache intochannels, sets, and ways, but does not address individual sectors withinways. Given the lack of addressable sectors within a page cache,implementations of a page cache call for a cache line from a way of asector-based cache to be cleaned before migrating to the page cache.Duplicating an entire cache line to provide reliability for dirty datais inefficient. Additionally, implementations of a page cache write anentire cache line to non-volatile memory upon eviction, cleaning, etc.As a result, any portion of the cache line that includes clean data isunnecessarily rewritten to non-volatile memory.

Aspects of the present disclosure address the above and other issues bytracking sector-based redundant copies dirty data within a page cache.For example, embodiments use the redundant write buffer metadata totrack sector-sized portions of cache lines in a page cache. As a result,dirty sectors of data do not need to be cleaned when migrated to thepage cache. Additionally, embodiments can write dirty data from the pagecache to non-volatile memory while omitting clean data from the samecache line.

FIG. 1 illustrates an example computing system 100 that includes amemory subsystem 110 in accordance with some embodiments of the presentdisclosure. The memory subsystem 110 can include media, such as one ormore volatile memory devices (e.g., memory device 140), one or morenon-volatile memory devices (e.g., memory device 130), or a combinationof such.

A memory subsystem 110 can be a storage device, a memory module, or ahybrid of a storage device and memory module. Examples of a storagedevice include a solid-state drive (SSD), a flash drive, a universalserial bus (USB) flash drive, an embedded Multi-Media Controller (eMMC)drive, a Universal Flash Storage (UFS) drive, a secure digital (SD)card, and a hard disk drive (HDD). Examples of memory modules include adual in-line memory module (DIMM), a small outline DIMM (SO-DIMM), andvarious types of non-volatile dual in-line memory module (NVDIMM).

The computing system 100 can be a computing device such as a desktopcomputer, laptop computer, network server, mobile device, a vehicle(e.g., airplane, drone, train, automobile, or other conveyance),Internet of Things (IoT) enabled device, embedded computer (e.g., oneincluded in a vehicle, industrial equipment, or a networked commercialdevice), or such computing device that includes memory and a processingdevice.

The computing system 100 can include a host system 120 that is coupledto one or more memory subsystems 110. In some embodiments, the hostsystem 120 is coupled to different types of memory subsystems 110. FIG.1 illustrates one example of a host system 120 coupled to one memorysubsystem 110. As used herein, “coupled to” or “coupled with” generallyrefers to a connection between components, which can be an indirectcommunicative connection or direct communicative connection (e.g.,without intervening components), whether wired or wireless, includingconnections such as electrical, optical, magnetic, and the like.

The host system 120 can include a processor chipset and a software stackexecuted by the processor chipset. The processor chipset can include oneor more cores, one or more caches, a memory controller (e.g., NVDIMMcontroller), and a storage protocol controller (e.g., PCIe controller,SATA controller). The host system 120 uses the memory subsystem 110, forexample, to write data to the memory subsystem 110 and read data fromthe memory subsystem 110.

The host system 120 can be coupled to the memory subsystem 110 via aphysical host interface. Examples of a physical host interface include,but are not limited to, a serial advanced technology attachment (SATA)interface, a peripheral component interconnect express (PCIe) interface,universal serial bus (USB) interface, Fibre Channel, Serial AttachedSCSI (SAS), Small Computer System Interface (SCSI), a double data rate(DDR) memory bus, a dual in-line memory module (DIMM) interface (e.g.,DIMM socket interface that supports Double Data Rate (DDR)), Open NANDFlash Interface (ONFI), Double Data Rate (DDR), Low Power Double DataRate (LPDDR), or any other interface. The physical host interface can beused to transmit data between the host system 120 and the memorysubsystem 110. The host system 120 can further utilize an NVM Express(NVMe) interface to access components (e.g., memory devices 130) whenthe memory subsystem 110 is coupled with the host system 120 by the PCIeinterface. The physical host interface can provide an interface forpassing control, address, data, and other signals between the memorysubsystem 110 and the host system 120. FIG. 1 illustrates a memorysubsystem 110 as an example. In general, the host system 120 can accessmultiple memory subsystems via a same communication connection, multipleseparate communication connections, and/or a combination ofcommunication connections.

The memory devices 130, 140 can include any combination of the differenttypes of non-volatile memory devices and/or volatile memory devices. Thevolatile memory devices (e.g., memory device 140) can be, but are notlimited to, random-access memory (RAM), such as static random-accessmemory (SRAM), dynamic random-access memory (DRAM), and synchronousdynamic random-access memory (SDRAM). For example, memory devices 140can implement one or more caches.

Some examples of non-volatile memory devices (e.g., memory device 130)include negative-and (NAND) type flash memory and write-in-place memory,such as a three-dimensional cross-point (“3D cross-point”) memorydevice, which is a cross-point array of non-volatile memory cells. Across-point array of non-volatile memory can perform bit storage basedon a change of bulk resistance, in conjunction with a stackablecross-gridded data access array. Additionally, in contrast to manyflash-based memories, cross-point non-volatile memory can perform awrite in-place operation, where a non-volatile memory cell can beprogrammed without the non-volatile memory cell being previously erased.NAND type flash memory includes, for example, two-dimensional NAND (2DNAND) and three-dimensional NAND (3D NAND).

Each of the memory devices 130 can include one or more arrays of memorycells. One type of memory cell, for example, single-level cells (SLC)can store one bit per cell. Other types of memory cells, such asmulti-level cells (MLCs), triple-level cells (TLCs), and quad-levelcells (QLCs), can store multiple bits per cell. In some embodiments,each of the memory devices 130 can include one or more arrays of memorycells such as SLCs, MLCs, TLCs, QLCs, or any combination of such. Insome embodiments, a particular memory device can include an SLC portion,and an MLC portion, a TLC portion, or a QLC portion of memory cells. Thememory cells of the memory devices 130 can be grouped as pages that canrefer to a logical unit of the memory device used to store data. Withsome types of memory (e.g., NAND), pages can be grouped to form blocks.

Although non-volatile memory devices such as NAND type memory (e.g., 2DNAND, 3D NAND) and 3D cross-point array of non-volatile memory cells aredescribed, the memory device 130 can be based on any other type ofnon-volatile memory, such as read-only memory (ROM), phase change memory(PCM), self-selecting memory, other chalcogenide based memories,ferroelectric transistor random-access memory (FeTRAM), ferroelectricrandom-access memory (FeRAM), magneto random-access memory (MRAM), SpinTransfer Torque (STT)-MRAM, conductive bridging RAM (CBRAM), resistiverandom-access memory (RRAM), oxide based RRAM (OxRAM), negative-or (NOR)flash memory, and electrically erasable programmable read-only memory(EEPROM).

A memory subsystem controller 115 (or controller 115 for simplicity) cancommunicate with the memory devices 130 to perform operations such asreading data, writing data, or erasing data at the memory devices 130and other such operations (e.g., in response to commands scheduled on acommand bus by controller 115). The memory subsystem controller 115 caninclude hardware such as one or more integrated circuits and/or discretecomponents, a buffer memory, or a combination thereof. The hardware caninclude digital circuitry with dedicated (i.e., hard-coded) logic toperform the operations described herein. The memory subsystem controller115 can be a microcontroller, special purpose logic circuitry (e.g., afield programmable gate array (FPGA), an application specific integratedcircuit (ASIC), etc.), or another suitable processor.

The memory subsystem controller 115 can include a processing device 117(processor) configured to execute instructions stored in a local memory119. In the illustrated example, the local memory 119 of the memorysubsystem controller 115 includes an embedded memory configured to storeinstructions for performing various processes, operations, logic flows,and routines that control operation of the memory subsystem 110,including handling communications between the memory subsystem 110 andthe host system 120.

In some embodiments, the local memory 119 can include memory registersstoring memory pointers, fetched data, etc. The local memory 119 canalso include read-only memory (ROM) for storing micro-code. While theexample memory subsystem 110 in FIG. 1 has been illustrated as includingthe memory subsystem controller 115, in another embodiment of thepresent disclosure, a memory subsystem 110 does not include a memorysubsystem controller 115, and can instead rely upon external control(e.g., provided by an external host, or by a processor or controllerseparate from the memory subsystem).

In general, the memory subsystem controller 115 can receive commands oroperations from the host system 120 (e.g., read and write commands) andcan convert the commands or operations into instructions or appropriatecommands to achieve the desired access to the memory devices 130 and/orthe memory device 140. The memory subsystem controller 115 can beresponsible for other operations such as wear leveling operations,garbage collection operations, error detection and error-correcting code(ECC) operations, encryption operations, caching operations, and addresstranslations between a logical address (e.g., logical block address(LBA), namespace) and a physical address (e.g., physical block address)that are associated with the memory devices 130. The memory subsystemcontroller 115 can further include host interface circuitry tocommunicate with the host system 120 via the physical host interface.The host interface circuitry can convert the commands received from thehost system into command instructions to access the memory devices 130and/or the memory device 140 as well as convert responses associatedwith the memory devices 130 and/or the memory device 140 intoinformation for the host system 120.

The memory subsystem 110 can also include additional circuitry orcomponents that are not illustrated. In some embodiments, the memorysubsystem 110 can include a cache or buffer (e.g., DRAM) and addresscircuitry (e.g., a row decoder and a column decoder) that can receive anaddress from the controller 115 and decode the address to access thememory devices 130.

In some embodiments, the memory devices 130 include local mediacontrollers 135 that operate in conjunction with memory subsystemcontroller 115 to execute operations on one or more memory cells of thememory devices 130. An external controller (e.g., memory subsystemcontroller 115) can externally manage the memory device 130 (e.g.,perform media management operations on the memory device 130). In someembodiments, a memory device 130 is a managed memory device, which is araw memory device combined with a local controller (e.g., localcontroller 135) for media management within the same memory devicepackage. An example of a managed memory device is a managed NAND (MNAND)device.

The memory subsystem 110 includes a redundant write buffer manager 113that can efficiently maintain and track redundant copies of dirty datawithin the cache. In some embodiments, the controller 115 includes atleast a portion of the redundant write buffer manager 113. For example,the controller 115 can include a processor 117 (processing device)configured to execute instructions stored in local memory 119 forperforming the operations described herein. In some embodiments, theredundant write buffer manager 113 is part of the host system 110, anapplication, or an operating system. In some embodiments, the memorydevices 130 can be managed memory devices (e.g., managed NAND), which isa raw memory device combined with a local controller 130 for memorymanagement within the same memory device package. A local controller 130can include a redundant write buffer manager 113.

The redundant write buffer manager 113 can maintain and track redundantcopies of dirty data within the cache. In particular, the redundantwrite buffer manager 113 can repurpose cache lines to create andmaintain redundant write buffers and use the redundant write buffers torecover dirty data and manage data migration to and from a cache.Further details with regards to the operations of the redundant writebuffer manager 113 are described below.

FIG. 2 illustrates an example of redundant write buffers within a cache200. In one embodiment, the cache 200 is implemented using a pluralityof memory devices 140. The illustrated portion of the cache 200 includestwo channels, four sets per channel, and four ways per set. For example,each channel can connect the memory subsystem controller 115 to aseparate set of one or more memory devices 140. The portions of thememory devices 140 that make up the cache 200 are addressable using achannel value, a set value, and a way value. In a sector-based cache,each way is further divisible into sectors. For example, a cache linecan refer to data written to the four sectors of a given way asillustrated. Additionally, a sector-based version of the cache 200 canmaintain metadata (e.g., indicating whether the data is dirty) persector. This metadata can be stored in tags, as described with referenceto FIG. 5 . In a page cache, however, such metadata is conventionallymaintained per way (or cache line), but not per sector. Such cachelines, however, are still accessible in smaller chunks—e.g., 64-byte,sector-sized portions of data. As such, for the ease of explanationbelow, the use of “sector” refers to a sector-sized portion of a way orcache line, whether or not said portion is within a sector-based cache.

In one embodiment, a sector can store 64 bytes of data in the cache 200.Using this simple illustration, it follows that a cache line consuming away can store 256 bytes of data. Other divisions of the cache 200 arepossible. In one embodiment, a cache line stores 1 kilobyte of datasubdivided into 16 sectors, 2 kilobytes of data subdivided into 32sectors, or another configuration including a different sector sizeand/or a different number of sectors.

The cache 200 includes original copies of written dirty data (e.g.,W0-W6), duplicate or redundant copies of dirty data (e.g., D0-D6), andredundant write buffer metadata (e.g., T0-T3). The redundant writebuffer metadata indicates when a cache line has been repurposed to serveas a redundant write buffer. For example, the metadata can include aflag or other indicator to demonstrate that the cache line is currentlya redundant write buffer. As a result, redundant write buffers can bedynamically added and removed as needed.

In one embodiment, the redundant write buffer metadata further includesa mapping between original and redundant copies of data. For example,the metadata can include, in a position associated with a sector of theredundant write buffer, the way value and/or the sector value of thecorresponding original copy of the dirty data. Furthermore, the channelvalue and set value of the original copy of the dirty data can bedetermined inherently based upon the channel and set values of theredundant write buffer.

In one embodiment, the redundant write buffer manager 113 creates andmaintains a redundant write buffer for each set of the cache 200 bymaintaining a 1:1 relationship between a set storing original data andthe set storing duplicate data. For example, the redundant write buffermanager 113 can maintain redundant write buffer metadata in a set havingthe same set value as the set storing the original data, but ondifferent channel (e.g., set 0 of channel 1 can store redundant writebuffer metadata for original data stored in set 0 of channel 0). Inanother embodiment, the redundant write buffer manager 113 maintains aone-to-many relationship between the location of the redundant writebuffer metadata and the original data (e.g., set 0 of channel 1 canstore redundant write buffer metadata for original data stored inmultiple sets of channel 0). Embodiments of these mappings are describedfurther with reference to FIGS. 3-6 .

FIG. 3 illustrates an example organization of metadata for a redundantwrite buffer. As described above, in addition to an indicator todemonstrate that the cache line is currently a redundant write buffer,the metadata can include mappings between original and redundant copiesof data. Embodiments can store these mappings in a sector of therepurposed cache line as a table or another data structure (e.g., T0,T1, T2, or T3). In one embodiment, an order or other format of themetadata correlates to the other sectors of the redundant write buffer.As illustrated, buffer sector 0 is the metadata entry that refers to theleast significant sector value in the corresponding way of the redundantwrite buffer, buffer sector 1 is the metadata entry that refers to thenext least significant sector value in the corresponding way of theredundant write buffer, etc.

In one embodiment, the metadata mapping a redundant copy of dirty datato the original copy of dirty write data includes a way value and asector value indicating the location of the original dirty data withinthe way. The set value and channel value of the redundant write buffercan map to the set value and channel value of the dirty write data byway of a consistent relationship. For example, the two channel valuescan follow a rule of always differing by a value of 1 while the setvalues can be the same. If dirty data is written to channel 0, set 0,such an embodiment would use a way in channel 1, set 0 to maintain aredundant write buffer. Using different channels can provide datareliability when, e.g., the original data is inaccessible due to afailure that impacts an entire channel of the cache 200. Using the samevalue for the sets minimizes the amount of processing or storage neededto map redundant copies to original copies. Other consistentrelationships between channel values and set values in the mapping,however, can be implemented.

FIG. 4 illustrates an example of metadata for a redundant write bufferas shown in FIG. 2 . In particular, this example shows the datastructure T0 stored in channel 1, set 0, way 3, sector 3 of the cache200. The entry labeled buffer sector 0 corresponds to the leastsignificant sector of the repurposed cache line, channel 1, set 0, way3, sector 0. This entry includes a way value of 1 and a sector value of2. Implicitly, this entry maps to channel 0, set 0 using therelationship examples above. The metadata in this entry, therefore, mapsthe redundant copy of dirty data stored in channel 1, set 0, way 3,sector 0, D0, to the original copy of dirty data stored in channel 0,set 0, way 0, sector 1, W0. The entry labeled buffer sector 1 maps theredundant copy of dirty stored in channel 1, set 0, way 3, sector 1, D2,to the original copy of dirty data stored in channel 0, set 0, way 2,sector 2, W2. The entry labeled buffer sector 2 maps the redundant copyof dirty stored in channel 1, set 0, way 3, sector 2, D3, to theoriginal copy of dirty data stored in channel 0, set 0, way 1, sector 2,W3.

In one embodiment, the data structure mapping original dirty data toredundant copies in a redundant write buffer includes mappings formultiple ways. As such, the format of the data structure storing theredundant write buffer metadata provides for mappings of sectors of themultiple ways. For example, if there was sufficient space in the sectorholding T0, the mappings could include an entry for channel 1, set 0,way 2, sector 0 (storing the duplicate data D5). In another embodiment,the data structure is contained to mappings for the same way and sectorsof another way are mapped by a data structure within that way—e.g., T1in channel 1, set 0, way 2, sector 3 can provide mapping metadata forD5.

FIG. 5 illustrates another example organization of metadata for aredundant write buffer. As described above, a tag can store metadata fora way or sectors within that way, if the cache is a sector-based cache.For example, tags can include indicators of whether sectors within a waystore dirty data. In addition to repurposing a way from ordinary use asa cache line into a redundant write buffer, embodiments can alsorepurpose tags for the corresponding ways. In one embodiment, there issufficient space in the tags to store at least some of the mappingmetadata in addition to, e.g., indicators/valid bits to track whichsectors of the redundant write buffer are currently in use. Some spacecan be freed by removing the redundancy of dirty status indicators inthe non-repurposed tags. For example, the existence of a redundant copyof dirty data can be used to indicate that an original copy stores dirtydata. The tag of the original copy of the dirty data, therefore, canfree at least one tag bit that would have been used for tracking dirtystatus to be used for mapping redundant dirty data.

In an embodiment that repurposes these tags, instead of storing way,sector value pairs in a data structure within a sector of the redundantwrite buffer, the data structure is moved, in whole or part, to the tagor tags for the way repurposed as a redundant write buffer. As a result,embodiments can store a greater number of metadata mappings in a singlesector of a redundant write buffer, freeing up other sectors within theset to serve as a part of the redundant write buffer in storingredundant copies of dirty data.

The number of ways per set and sectors per way in the cache can dictatethe number of bits needed to track way, sector value pairs and, in turn,impact how much of the redundant data mappings is stored in tags. Forexample, reducing the number of ways per set from 8 to 4 results in areduction from 3 bits to track way values to 2 bits to track way values.In one embodiment, increasing the number of channels in the cacheresults in fewer ways per set.

In the illustrated example, way values are moved into the metadata tagsof a redundant write buffer while sector values remain in a sector ofthe redundant write buffer. As a result, the tag stores a way value foreach sector of dirty data in the redundant write buffer—e.g., bymaintaining a format that maps a position of the value in the datastructure to a sector in the set that stores a redundant copy of dirtydata. In one embodiment, the metadata tags include way values (asillustrated) in addition to valid bits (not illustrated). The metadatasector (e.g., set 3, way 0, sector 3) stores a sector value for eachsector of dirty data in the write buffer—e.g., by also maintaining aformat that maps a position of the value in the data structure to asector in the set. The combination of the tag and metadata sector servesas the redundant write buffer metadata data structure and provides amapping between redundant copies of dirty data stored the correspondingsectors within the redundant write buffer for that set to the originalcopies of the dirty data.

FIG. 6 illustrates yet another example organization of metadata for aredundant write buffer. As described above, a page cache tracks lessgranular metadata (e.g., a dirty indicator per way rather than persector). Such a design often results in less bits of metadata availableto be repurposed in the implementation of a redundant write buffer. Atag, therefore, can have fewer bits available for tracking thevalid/invalid status of redundant write buffer sectors. As a result,embodiments can include at least some validity status indicators in thesector of the redundant write buffer that is repurposed to storemetadata.

In the illustrated example, the tags have insufficient space to storemetadata for validity indicators for each buffer sector. The tag storesvalidity indicators for a portion of the redundant write buffer. Forexample, the tag can store half of the valid bits for the sectors of theredundant write buffer. The remaining validity indicators are stored inthe metadata sector of the redundant write buffer. The illustratedoverflow for valid bits gives an example in which the valid bits consumeat least one portion of the metadata sector at way 0, set 3, sector 3,that would otherwise map to a way, sector value pair.

In one embodiment, the tag includes an identifier to indicate whichportion of the sectors are represented the tag's valid bits. Continuingthe example in which a tag can store half of the valid bits for thesectors of a redundant write buffer, the portion identifier (ID) canindicate whether the tag store valid bits for the first half of sectorsor the second half of sectors. In another embodiment, the tagconsistently stores the same portion of valid bits and omits the portionID.

In one embodiment, the tag includes a partial valid count to representthe number of valid sectors represented by valid indicators storedoutside of the tag. Embodiments can count the number of valid sectorsrepresented by the portion of valid bits in the tag and combine thatcount with the partial valid count to determine, e.g., how many dirtysectors are stored by the redundant write buffer. In one embodiment, theredundant write buffer manager 113 uses this total count, when itsatisfies a condition or threshold, to trigger a cleaning operation tofree up buffer space.

FIG. 7 is a flow diagram of an example method 700 to write redundantdirty data to a cache in accordance with some embodiments of the presentdisclosure. The method 700 can be performed by processing logic that caninclude hardware (e.g., processing device, circuitry, dedicated logic,programmable logic, microcode, hardware of a device, integrated circuit,etc.), software (e.g., instructions run or executed on a processingdevice), or a combination thereof. In some embodiments, the method 700is performed by the redundant write buffer manager 113 of FIG. 1 .Although shown in a particular sequence or order, unless otherwisespecified, the order of the processes can be modified. Thus, theillustrated embodiments should be understood only as examples, and theillustrated processes can be performed in a different order, and someprocesses can be performed in parallel. Additionally, one or moreprocesses can be omitted in various embodiments. Thus, not all processesare required in every embodiment. Other process flows are possible.

At operation 705, the processing device receives or otherwise detects anoperation to write dirty data to the cache. For example, the host system120 can direct write requests to the memory subsystem 110. The memorysubsystem controller 115 determines that the write request is directedto data currently stored in a cache implemented in the memory device140. Using the cache 200 illustrated in FIG. 2 as an example, theprocessing device receives or detects a write of dirty data directed tothe cache line stored at channel 0, set 0, way 0, sector 1.

At operation 710, the processing device writes the dirty data to theidentified cache line. Continuing the example above using the cache 200,the written data is illustrated as W0. In one embodiment, the processingdevice updates the metadata for the written sector(s) to indicate thatthe sector(s) are currently storing dirty data. For example, theprocessing device sets a dirty bit or otherwise updates an indicator inthe tag corresponding to the recently written cache line.

At operation 715, the processing device determines if there is anexisting redundant write buffer corresponding to the selected cache linewritten with dirty data. In one embodiment, the cache is initially(e.g., at startup) allocated without any redundant write buffers. Duringoperation, the processing device can dynamically repurpose one or wayswithin the cache to serve as a redundant write buffer. Additionally,when a way is no longer needed to store redundant write data, theprocessing device can return the way to ordinary cache space. As aresult, the processing device is able to dynamically scale the redundantwrite buffer space based upon the current need of the workflow managedby the cache, reducing the storage space cost of providing dirty datareliability.

Continuing the example of dirty data W0 written to channel 0, set 0, way0, sector 1, the processing device looks for the existence of aredundant write buffer in channel 1, set 0. Embodiments, however, arenot limited to searching for a redundant write buffer within the sethaving the same set value as the original data but on a differentchannel. In some embodiments, the processing device searches anotherpredictable set for the redundant write buffer or the processing devicesearches multiple sets for the redundant write buffer (e.g., when aredundant write buffer maintains metadata for multiple sets). Asdescribed above, embodiments can use a metadata, such as a buffer bit,to indicate the existence of a redundant write buffer. Embodiments canmaintain this indicator in a sector of the repurposed cache line or inthe corresponding tag.

In addition to identifying an existing redundant write buffer, theprocessing device can determine if the existing write buffer alreadycontains old data for the corresponding sector (e.g., to be overwritten)or available space in the buffer to write a redundant copy of the dirtydata. For example, when data can be overwritten, the processing deviceparses the metadata maintained for the buffer to determine if any way,sector value pairs match the way, sector value pair for the recentlywritten dirty data. Otherwise, or if a match is not found, theprocessing device looks for a sector in an existing buffer that does notcontain valid data.

In one embodiment, the processing device fills a redundant buffer in alinear manner. For example, as the processing device adds redundant datato the buffer, it follows a predetermined order, such as starting withthe least significant sector value and searching for an invalid sectorin increasing order of sector values. When the processing device evictsor otherwise invalidates redundant data, the processing devicecompresses remaining valid sectors toward the least significant sectors.If new dirty data is copied to the buffer for a sector that alreadystores a redundant copy of old dirty data, the processing device willread the most recent copy based upon the linear order when evicting orrecovering data.

If there is not an existing redundant write buffer for this cache line(e.g., metadata sectors T0 and T1 have yet to be written to createbuffer space) or there is not an existing buffer with available space,the method 700 proceeds to operation 720 to repurpose a cache line toserve as a buffer. If there is an existing redundant write buffer (e.g.,metadata sector T0 has been written, repurposing the cache line at way 3to serve as a buffer), the method 700 proceeds to operation 730.

At operation 720, the processing device selects an available way/cacheline to create a new redundant write buffer. For example, the processingdevice looks for an empty way in a set having the same set value as theoriginal copy of the dirty data, but on a different channel. For thedirty data W0, the processing device would look for an available way inchannel 1, set 0. The processing device can search for an available wayfrom the most significant way value to the least significant way value,from the least significant to the most significant, or via anothersearch method. If way 3 had yet to be repurposed and written withredundant data, this operation could select way 3 to serve as aredundant write buffer.

At operation 725, the processing device updates the metadata for theavailable cache line to repurpose this portion of the cache to serve asa redundant write buffer. For example, the processing device can set abit or otherwise update an indicator in the tag or a newly designatedmetadata sector (e.g., T0 in sector 3) to demonstrate that way 3 is nowa redundant write buffer. As described above, such an indication canapply to multiple ways. For example, the indicator can demonstrate thatboth ways 2 and 3 serve as a redundant write buffer.

At operation 730, the processing device writes a redundant copy of thedirty data to a portion of the redundant write buffer. For example, theprocessing device writes (or overwrites) sector 0 of way 3 with aredundant copy D0 of the dirty data W0.

At operation 735, the processing device updates a redundant write buffermetadata entry to reference the original location of the dirty data. Forexample, the processing device can update one or both of the metadatasector T0 and the tag for way 3, sector 0, to store the way, sectorvalue pair (0, 1) for the original copy of the dirty data W0. Thisupdate creates a mapping between the original and redundant copies ofthe dirty data. Additionally, the processing device can update themetadata to indicate that the redundant copy of the dirty data is valid.

FIG. 8 is a flow diagram of an example method 800 to recover data usinga redundant write buffer in accordance with some embodiments of thepresent disclosure. The method 800 can be performed by processing logicthat can include hardware (e.g., processing device, circuitry, dedicatedlogic, programmable logic, microcode, hardware of a device, integratedcircuit, etc.), software (e.g., instructions run or executed on aprocessing device), or a combination thereof. In some embodiments, themethod 800 is performed by the redundant write buffer manager 113 ofFIG. 1 . Although shown in a particular sequence or order, unlessotherwise specified, the order of the processes can be modified. Thus,the illustrated embodiments should be understood only as examples, andthe illustrated processes can be performed in a different order, andsome processes can be performed in parallel. Additionally, one or moreprocesses can be omitted in various embodiments. Thus, not all processesare required in every embodiment. Other process flows are possible.

At operation 805, the processing device receives or otherwise detects aread request for cached data. For example, the host system 120 candirect read requests to the memory subsystem 110. The memory subsystemcontroller 115 determines that the read request is directed to datacurrently stored in a cache implemented in the memory device 140. Usingthe cache 200 illustrated in FIG. 2 as an example, the processing devicereceives or detects a read request for the data W0 in the cache linestored at channel 0, set 0, way 0, sector 1. In response to the readrequest, the processing device attempts to read this sector.

At operation 810, the processing device determines if the operationsuccessfully read the cached data. For example, the processing devicecan use an error detection and correction algorithm when reading thesector storing the data. If the error detection and correction algorithmindicates that the data was successfully decoded/read, the method 800proceeds to operation 815. If the error detection and correctionalgorithm indicates that the data was not successfully decoded/read, themethod 800 proceeds to operation 820.

At operation 815, the processing device returns the data in response tothe read request. For example, the memory subsystem 115 directs the dataread from the cache to the host system 120 in response to the receivedread request.

At operation 820, the processing device determines if the failed readoperation was directed to clean data. As discussed above, tags forsectors or ways of the cache can include metadata indicating the cleanor dirty status of the corresponding portion of the cache.Alternatively, the existence of a redundant data buffer entry for theoriginal cache location can serve as an indication that the data wasdirty. The detection of a redundant data buffer entry for the originalcache location is described below. If the data that could not besuccessfully read from the original cache location was clean, the method800 proceeds to operation 825. If the data that could not besuccessfully read from the original cache location was dirty, the method800 proceeds to operation 835.

At operation 825, the processing device reads the clean data from anon-volatile memory. For example, if the processing device fails inattempting to read W0 from channel 0, set 0, way 0, sector 1, but saiddata was copied from or had been copied to an underlying non-volatilememory device 130, the processing device treats the cache read as a missand reads the clean data from the non-volatile memory device 130.

At operation 830, the processing device optionally writes the recovereddata to the original cache location to correct the failure. For example,if the processing device determines that the failure does not yetsatisfy a threshold (e.g., number of failed reads, severity of failure,etc.), the processing device can attempt to continue using the sector.Alternatively, the processing device marks the original cache locationas a bad location to prevent future use that can lead to data loss.Furthermore, the processing device returns the data at operation 815, asdescribed above.

At operation 835, the processing device uses the original cache locationto locate and read a redundant copy of the dirty data within the cache.In one embodiment, the processing device can locate a redundant writebuffer for dirty data in the set having the same value as the originalcopy, but on a different channel. The processing device parses this setfor a way marked as a redundant write buffer and searches thecorresponding metadata for an entry for the original data location. Theprocessing device reads the redundant copy of the dirty data from thesector corresponding to the located metadata.

For example, upon a failure to read the original copy of the dirty dataW0 at channel 0, set 0, way 0, sector 1, the processing device parsesthe ways in channel 1, set 0 to locate a redundant write buffer. Theprocessing device detects that channel 1, set 0, way 3 is flagged as aredundant write buffer based upon a metadata indicator and parses themetadata entries, e.g., the data structure T0 stored in sector 3. Thedata structure T0 includes an entry with the way, sector pair (0, 1)that matches the location of the original dirty data W0. The metadataentry is in a position with the data structure T0 that corresponds toduplicate data D0 stored in channel 1, set 0, way 3, sector 0. Theprocessing device reads this duplicate data D0 to fulfill the readrequest.

At operation 840, the processing device optionally writes the dirty datafrom the redundant copy to the non-volatile memory. Given that thisdirty data no longer has the benefit of redundancy, a data reliabilitypolicy can direct the processing device to write the data to anon-volatile memory device 130 to prevent data loss. The method 800 canoptionally proceed to operation 830, as described above, in addition toreturning the data at operation 815.

FIG. 9 is a flow diagram of an example method 900 to track the migrationof dirty data between caches using a redundant write buffer inaccordance with some embodiments of the present disclosure. The method900 can be performed by processing logic that can include hardware(e.g., processing device, circuitry, dedicated logic, programmablelogic, microcode, hardware of a device, integrated circuit, etc.),software (e.g., instructions run or executed on a processing device), ora combination thereof. In some embodiments, the method 900 is performedby the redundant write buffer manager 113 of FIG. 1 . Although shown ina particular sequence or order, unless otherwise specified, the order ofthe processes can be modified. Thus, the illustrated embodiments shouldbe understood only as examples, and the illustrated processes can beperformed in a different order, and some processes can be performed inparallel. Additionally, one or more processes can be omitted in variousembodiments. Thus, not all processes are required in every embodiment.Other process flows are possible.

At operation 905, the processing device identifies a cache line to beevicted from one cache to another. For example, the memory subsystem 110can implement a cache hierarchy with multiple levels of caches withinthe memory devices 140. The cache levels can include a level-one (L1)processor cache, a level-two (L2) sectored cache, and a level-three (L3)page cache. In such layered approach, e.g., the memory subsystem 110 canevict a cache line from the sectored cache and write the cache line tothe page cache.

In one embodiment, the processing device evicts a cache line in responseto a trigger event. For example, a trigger can include when an amount ofspace available for caching data satisfies a threshold value. A need foradditional space to store new data can trigger the eviction (orcleaning/flushing) of previously cached data. In evicting previouslycached data, the processing device will invalidate redundant copies ofdirty data stored in one or more redundant write buffers. As anotherexample, a need for additional redundant buffer space to store new dirtydata duplicates can trigger the eviction of previously cached dirtydata. When the available space in a redundant write buffer satisfies athreshold value, the processing device cleans or evicts cache lines withdirty data duplicated to the redundant write buffer, thus removing aneed to store duplicate dirty data for the cleaned/evicted data.

At operation 910, the processing device copies the cache line from thesectored cache to the page cache. As described above, a page cachemaintains limited metadata in comparison to a sectored cache. Forexample, a conventional page cache tag can maintain a dirty/cleanindicator for a cache line but may not include dirty/clean indicatorsfor each sector. Caches implementing a redundant write buffer asdescribed above, however, can track the dirty/clean status of sectorsoutside of the tag metadata. As such, the processing device can copy thecache line containing dirty data from the sectored cache to the pagecache without cleaning the data and while continuing to track thedirty/clean status of individual sectors. In copying the data from thesectored cache to the page cache, the processing device invalidates thecache line and redundant copies in the sectored cache.

At operation 915, the processing device writes a redundant copy of eachdirty sector to another portion of the page cache. For example, theprocessing device can utilize operations 715-730 as described above toadd a redundant copy of dirty data to a redundant write buffer.

At operation 920, the processing device marks each redundant copy asvalid and updates the redundant write buffer metadata to map theredundant copy of the dirty data to the original copy of the dirty data.For example, the processing device can utilize operation 735 asdescribed above to update the metadata for the redundant copy of dirtydata.

FIG. 10 is a flow diagram of an example method 1000 to copy dirty datato non-volatile media using a redundant write buffer in accordance withsome embodiments of the present disclosure. The method 1000 can beperformed by processing logic that can include hardware (e.g.,processing device, circuitry, dedicated logic, programmable logic,microcode, hardware of a device, integrated circuit, etc.), software(e.g., instructions run or executed on a processing device), or acombination thereof. In some embodiments, the method 1000 is performedby the redundant write buffer manager 113 of FIG. 1 . Although shown ina particular sequence or order, unless otherwise specified, the order ofthe processes can be modified. Thus, the illustrated embodiments shouldbe understood only as examples, and the illustrated processes can beperformed in a different order, and some processes can be performed inparallel. Additionally, one or more processes can be omitted in variousembodiments. Thus, not all processes are required in every embodiment.Other process flows are possible.

At operation 1005, the processing device identifies a cache line to beevicted, flushed, or cleaned. As described above, the memory subsystem110 can implement a cache hierarchy with multiple levels of cacheswithin the memory devices 140. Based upon similar triggers as discussedabove, the processing device evicts, flushes, or cleans data by copyingdirty data from the page cache in volatile memory 140 to the underlyingnon-volatile memory 130.

At operation 1010, the processing device determines if the cache storesmetadata for a redundant copy of any dirty data in the cache line. Giventhat a page cache does not store a dirty/clean indicator for sectors ina tag for the cache line, the processing device identifies dirty sectorsby parsing the redundant write buffer metadata. If the processing devicefails to locate any dirty data “sectors” (sector-sized portions of thecache line being evicted) referenced by location in the metadata, themethod 1000 proceeds to operation 1015. Alternatively, if the tag forthe cache line being evicted indicates that the entire cache line isclean, the method 1000 proceeds to operation 1015. If the processingdevice locates one or more sectors referenced by location in themetadata, the method 1000 proceeds to operation 1020.

At operation 1015, the processing device processes the operation withoutcopying the cache line data to the non-volatile memory 130. Given thatthe cache line includes no dirty data, no data needs to be copied to thenon-volatile memory 130 and the cache line can be invalidated orotherwise processed for eviction.

At operation 1020, the processing device uses the detected metadata tocopy the dirty portion of the cache line to the non-volatile memorydevice 130 while omitting clean data. For example, the processing deviceuses the dirty data locations referenced by the redundant write buffermetadata to copy the sectors of dirty data from the cache line to thenon-volatile memory 130. Any remaining data in the cache line, beingclean, does not need to be copied to the non-volatile memory 130.Additionally, the cache line can be invalidated or otherwise processedfor eviction.

At operation 1025, the processing device updates the metadata for theredundant copies of dirty data as invalid. With the original dirty databeing evicted, flushed, or otherwise cleaned, the processing device canfree up the redundant write buffer space that stored the redundantcopies. For example, the processing device can update a bit or otherindicator in a tag for repurposed cache line to demonstrate that the oneor more sectors are now invalid.

FIG. 11 illustrates an example machine of a computer system 1100 withinwhich a set of instructions, for causing the machine to perform any oneor more of the methodologies discussed herein, can be executed. In someembodiments, the computer system 1100 can correspond to a host system(e.g., the host system 120 of FIG. 1 ) that includes, is coupled to, orutilizes a memory subsystem (e.g., the memory subsystem 110 of FIG. 1 )or can be used to perform the operations of a controller (e.g., toexecute an operating system to perform operations corresponding to theredundant write buffer manager 113 of FIG. 1 ). In alternativeembodiments, the machine can be connected (e.g., networked) to othermachines in a LAN, an intranet, an extranet, and/or the Internet. Themachine can operate in the capacity of a server or a client machine inclient-server network environment, as a peer machine in a peer-to-peer(or distributed) network environment, or as a server or a client machinein a cloud computing infrastructure or environment.

The machine can be a personal computer (PC), a tablet PC, a set-top box(STB), a Personal Digital Assistant (PDA), a cellular telephone, a webappliance, a server, a network router, a switch or bridge, or anymachine capable of executing a set of instructions (sequential orotherwise) that specify actions to be taken by that machine. Further,while a single machine is illustrated, the term “machine” shall also betaken to include any collection of machines that individually or jointlyexecute a set (or multiple sets) of instructions to perform any one ormore of the methodologies discussed herein.

The example computer system 1100 includes a processing device 1102, amain memory 1104 (e.g., read-only memory (ROM), flash memory, dynamicrandom-access memory (DRAM) such as synchronous DRAM (SDRAM) or RambusDRAM (RDRAM), etc.), a static memory 1106 (e.g., flash memory, staticrandom-access memory (SRAM), etc.), and a data storage system 1118,which communicate with each other via a bus 1130.

Processing device 1102 represents one or more general-purpose processingdevices such as a microprocessor, a central processing unit, or thelike. More particularly, the processing device can be a complexinstruction set computing (CISC) microprocessor, reduced instruction setcomputing (RISC) microprocessor, very long instruction word (VLIW)microprocessor, or a processor implementing other instruction sets, orprocessors implementing a combination of instruction sets. Processingdevice 1102 can also be one or more special-purpose processing devicessuch as an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA), a digital signal processor (DSP),network processor, or the like. The processing device 1102 is configuredto execute instructions 1126 for performing the operations and stepsdiscussed herein. The computer system 1100 can further include a networkinterface device 1108 to communicate over the network 1120.

The data storage system 1118 can include a machine-readable storagemedium 1124 (also known as a computer-readable medium) on which isstored one or more sets of instructions 1126 or software embodying anyone or more of the methodologies or functions described herein. Theinstructions 1126 can also reside, completely or at least partially,within the main memory 1104 and/or within the processing device 1102during execution thereof by the computer system 1100, the main memory1104 and the processing device 1102 also constituting machine-readablestorage media. The machine-readable storage medium 1124, data storagesystem 1118, and/or main memory 1104 can correspond to the memorysubsystem 110 of FIG. 1 .

In one embodiment, the instructions 1126 include instructions toimplement functionality corresponding to a redundant write buffermanager (e.g., the redundant write buffer manager 113 of FIG. 1 ). Whilethe machine-readable storage medium 1124 is shown in an exampleembodiment to be a single medium, the term “machine-readable storagemedium” should be taken to include a single medium or multiple mediathat store the one or more sets of instructions. The term“machine-readable storage medium” shall also be taken to include anymedium that is capable of storing or encoding a set of instructions forexecution by the machine and that cause the machine to perform any oneor more of the methodologies of the present disclosure. The term“machine-readable storage medium” shall accordingly be taken to include,but not be limited to, solid-state memories, optical media, and magneticmedia.

Some portions of the preceding detailed descriptions have been presentedin terms of algorithms and symbolic representations of operations ondata bits within a computer memory. These algorithmic descriptions andrepresentations are the ways used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of operations leading to adesired result. The operations are those requiring physicalmanipulations of physical quantities. Usually, though not necessarily,these quantities take the form of electrical or magnetic signals capableof being stored, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. The presentdisclosure can refer to the action and processes of a computer system,or similar electronic computing device, that manipulates and transformsdata represented as physical (electronic) quantities within the computersystem's registers and memories into other data similarly represented asphysical quantities within the computer system memories or registers orother such information storage systems.

The present disclosure also relates to an apparatus for performing theoperations herein. This apparatus can be specially constructed for theintended purposes, or it can include a general-purpose computerselectively activated or reconfigured by a computer program stored inthe computer. For example, a computer system or other data processingsystem, such as the controller 115, may carry out thecomputer-implemented methods 700-1000 in response to its processorexecuting a computer program (e.g., a sequence of instructions)contained in a memory or other non-transitory machine-readable storagemedium. Such a computer program can be stored in a computer readablestorage medium, such as, but not limited to, any type of disk includingfloppy disks, optical disks, CD-ROMs, and magnetic-optical disks,read-only memories (ROMs), random-access memories (RAMs), EPROMs,EEPROMs, magnetic or optical cards, or any type of media suitable forstoring electronic instructions, each coupled to a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general-purposesystems can be used with programs in accordance with the teachingsherein, or it can prove convenient to construct a more specializedapparatus to perform the method. The structure for a variety of thesesystems will appear as set forth in the description below. In addition,the present disclosure is not described with reference to any particularprogramming language. It will be appreciated that a variety ofprogramming languages can be used to implement the teachings of thedisclosure as described herein.

The present disclosure can be provided as a computer program product, orsoftware, that can include a machine-readable medium having storedthereon instructions, which can be used to program a computer system (orother electronic devices) to perform a process according to the presentdisclosure. A machine-readable medium includes any mechanism for storinginformation in a form readable by a machine (e.g., a computer). In someembodiments, a machine-readable (e.g., computer-readable) mediumincludes a machine (e.g., a computer) readable storage medium such as aread only memory (“ROM”), random-access memory (“RAM”), magnetic diskstorage media, optical storage media, flash memory components, etc.

In the foregoing specification, embodiments of the disclosure have beendescribed with reference to specific example embodiments thereof. Itwill be evident that various modifications can be made thereto withoutdeparting from the broader spirit and scope of embodiments of thedisclosure as set forth in the following claims. The specification anddrawings are, accordingly, to be regarded in an illustrative senserather than a restrictive sense.

What is claimed is:
 1. A method comprising: detecting an operation towrite dirty data to a cache, wherein the cache is divided into aplurality of channels; writing the dirty data to a first cache line inthe cache, wherein the first cache line is accessed via a first channel;determining there is not an existing write buffer for the first cacheline; selecting a second cache line accessible via a second channel, thefirst and second channels differing from one another; writing aredundant copy of the dirty data to the second cache line in the cache;and updating a metadata entry for the second cache line to reference alocation of the dirty data in the first cache line and to indicate thatthe second cache line is a redundant write buffer.
 2. The method ofclaim 1, wherein the cache is further divided into a plurality of waysand sectors, and wherein the metadata entry for the second cache line toreference the location of the dirty data in the first cache lineincludes a value for a way for the first cache line and a value for asector within the first cache line.
 3. The method of claim 2, whereinthe metadata entry for the second cache line to reference the locationof the dirty data in the first cache line is at least partially stored asector of the second cache line.
 4. The method of claim 1, wherein thecache is further divided into a plurality of sets addressed via setvalues and wherein the second cache line is selected for writing theredundant copy of the dirty data because the first and second cachelines have a same set value on different channels.
 5. The method ofclaim 1, wherein: the dirty data comprises data values marked as dirtyand the plurality of channels each comprise an addressable unit toconnect a memory subsystem to a set of one or more memory devices; andthe metadata entry for the second cache line associates the location ofthe dirty data in the first cache line with a location of the redundantcopy of the dirty data in the second cache line.
 6. The method of claim1, further comprising: detecting a failure of a read request directed tothe dirty data in the first cache line; in response to detecting thatthe failed read request was directed to dirty data, using the locationof the dirty data in the first cache line to locate and read theredundant copy of the dirty data in the second cache line; and returningthe dirty data in response to the read request.
 7. A non-transitorycomputer-readable storage medium comprising instructions that, whenexecuted by a processing device, cause the processing device to: detectan operation to write dirty data to a cache, wherein the cache isdivided into a plurality of channels; write the dirty data to a firstcache line in the cache, wherein the first cache line is accessed via afirst channel; determine there is not an existing write buffer for thefirst cache line; select a second cache line accessible via a secondchannel, the first and second channels differing from one another; writea redundant copy of the dirty data to the second cache line in thecache; and update a metadata entry for the second cache line toreference a location of the dirty data in the first cache line and toindicate that the second cache line is a redundant write buffer.
 8. Thenon-transitory computer-readable medium of claim 7, wherein the cache isfurther divided into a plurality of ways and sectors, and wherein themetadata entry for the second cache line to reference the location ofthe dirty data in the first cache line includes a value for a way forthe first cache line and a value for a sector within the first cacheline.
 9. The non-transitory computer-readable medium of claim 8, whereinthe metadata entry for the second cache line to reference the locationof the dirty data in the first cache line is at least partially stored asector of the second cache line.
 10. The non-transitorycomputer-readable medium of claim 7, wherein the cache is furtherdivided into a plurality of sets addressed via set values and whereinthe second cache line is selected for writing the redundant copy of thedirty data because the first and second cache lines have a same setvalue on different channels.
 11. The non-transitory computer-readablemedium of claim 7, wherein: the dirty data comprises data values markedas dirty and the plurality of channels each comprise an addressable unitto connect a memory subsystem to a set of one or more memory devices;and the metadata entry for the second cache line associates the locationof the dirty data in the first cache line with a location of theredundant copy of the dirty data in the second cache line.
 12. Thenon-transitory computer-readable medium of claim 7, wherein theprocessing device is further to: detect a failure of a read requestdirected to the dirty data in the first cache line; in response todetecting that the failed read request was directed to dirty data, usethe location of the dirty data in the first cache line to locate andread the redundant copy of the dirty data in the second cache line; andreturn the dirty data in response to the read request.
 13. Thenon-transitory computer-readable medium of claim 12, wherein theprocessing device is further to: in response to detecting that thefailed read request was directed to dirty data, write the dirty data tonon-volatile media.
 14. A system comprising: a plurality of memorycomponents; and a processing device, operatively coupled with theplurality of memory components, to: detect an operation to write dirtydata to a cache, wherein the cache is divided into a plurality ofchannels; write the dirty data to a first cache line in the cache,wherein the first cache line is accessed via a first channel; determinethere is not an existing write buffer for the first cache line; select asecond cache line accessible via a second channel, the first and secondchannels differing from one another; write a redundant copy of the dirtydata to the second cache line in the cache; and update a metadata entryfor the second cache line to reference a location of the dirty data inthe first cache line and to indicate that the second cache line is aredundant write buffer.
 15. The system of claim 14, wherein the cache isfurther divided into a plurality of ways and sectors, and wherein themetadata entry for the second cache line to reference the location ofthe dirty data in the first cache line includes a value for a way forthe first cache line and a value for a sector within the first cacheline.
 16. The system of claim 15, wherein the metadata entry for thesecond cache line to reference the location of the dirty data in thefirst cache line is at least partially stored a sector of the secondcache line.
 17. The system of claim 14, wherein the cache is furtherdivided into a plurality of sets addressed via set values and whereinthe second cache line is selected for writing the redundant copy of thedirty data because the first and second cache lines have a same setvalue on different channels.
 18. The system of claim 14, wherein: thedirty data comprises data values marked as dirty and the plurality ofchannels each comprise an addressable unit to connect a memory subsystemto a set of one or more memory devices; and the metadata entry for thesecond cache line associates the location of the dirty data in the firstcache line with a location of the redundant copy of the dirty data inthe second cache line.
 19. The system of claim 14, wherein theprocessing device is further to: detect a failure of a read requestdirected to the dirty data in the first cache line; in response todetecting that the failed read request was directed to dirty data, usethe location of the dirty data in the first cache line to locate andread the redundant copy of the dirty data in the second cache line; andreturn the dirty data in response to the read request.
 20. The system ofclaim 19, wherein the processing device is further to: in response todetecting that the failed read request was directed to dirty data, writethe dirty data to non-volatile media.